This invention relates to ultrasonic inspection apparatus, and, more particularly, to an ultrasonic inspection apparatus useful to perform through-thickness ultrasonic measurements of difficult-to-access articles.
Ultrasonic inspection is widely used to detect flaws in materials and structures. One type of flaw is delaminations between two of the multiple plies of composite material that are collated and then bonded together to form a composite structure. The delaminations may occur either during initial processing and fabrication, or during service. Such composite structures are widely used in aerospace and other applications, and there is a continuing concern with delaminations and other types of flaws.
In one type of ultrasonic inspection, termed through-thickness inspection, ultrasonic transducers are positioned in a facing relationship but contacting the opposite sides of a piece of the composite material that forms the composite structure. An ultrasonic signal is transmitted by one of the transducers, propagated through the piece of composite material, and received by the other transducer. The signal is analyzed by associated electronics. The presence and extent of flaws such as porosity and delaminations between the plies of the composite material sampled between the ultrasonic transducers may be assessed from the signal. For the analysis of many types of flaws in composite materials, only through-thickness ultrasonic measurements produce the required information. Reflection measurements wherein a single transducer is used are not operable to yield the required results.
Although this ultrasonic inspection approach is straightforward in principle, it is complicated by the fact that it is sometimes difficult to precisely position the ultrasonic transducers in a facing relation due to the confined spaces that are encountered in practice or because of the relative inaccessibility of one side of the composite article.
As an example, delamination flaws are sometimes found adjacent to access ports in hollow composite structures such as the outer bypass duct of a gas turbine aircraft engine. The flaws may be detected by disassembling the bypass duct structure from the engine and testing it using bench-type ultrasonic inspection apparatus in a testing laboratory. This testing is expensive and time consuming, and is not practical for many situations such as field inspections. As a result, the structure is not tested as thoroughly or as often as might otherwise be desired to check for the presence of flaws.
There is a need for an improved approach to the inspection of such composite structures, which is effective but easy and quick to perform. The present invention fulfills this need, and further provides related advantages.
The present invention provides an ultrasonic inspection apparatus and method for its use in through-thickness ultrasonic measurements of workpieces. The approach is particularly well suited for use in performing ultrasonic through-thickness measurements of difficult-to-access workpieces such as the walls of hollow structures. The approach achieves automatic alignment of the transmitting and receiving transducers. It avoids the need to disassemble the structure to otherwise permit access to both sides of the wall. The approach allows the determination of degradation of the integrity of the structure over time, so that the lifetime prior to repair or replacement may be estimated. The apparatus permits inspection around the entire periphery of an access opening, over a range of distances from the opening. The apparatus is relatively light in weight, so that it is hand held and may be positioned and operated by a single person.
An ultrasonic inspection apparatus comprises a yoke having a base, a first arm extending from the base, and a second arm extending from the base parallel to the first arm. There is a first ultrasonic transducer affixed to the first arm, a second ultrasonic transducer in facing relation to the first ultrasonic transducer, and a spring mount attaching the second ultrasonic transducer to the second arm. The spring mount comprises a spring biasing the second ultrasonic transducer toward the first ultrasonic transducer with a spring bias. A retractor, preferably a manual retractor, is affixed to the spring mount so as to permit the second ultrasonic transducer to be retracted away from the first ultrasonic transducer against the spring bias. In use of the apparatus an electronics system is in electrical communication with the first ultrasonic transducer and the second ultrasonic transducer. The electronics system transmits a driver signal to one of the ultrasonic transducers and receives a received signal from the other of the ultrasonic transducers.
A method for determining the presence of flaws in a composite material in a hollow structure comprises the step of furnishing a hollow structure having a wall comprising a piece of composite material. The wall has an interior surface, an exterior surface, and an access opening therethrough extending between the interior surface and the exterior surface. The hollow structure preferably comprises a component of an aircraft, more preferably a component of a gas turbine engine, and most preferably an outer bypass duct of a gas turbine engine. In the latter case, the access is an access port in the outer bypass duct. An ultrasonic inspection apparatus of the type described above is furnished. The ultrasonic inspection apparatus is positioned by the steps of placing one of the arms adjacent to the interior surface, one of the arms adjacent to the exterior surface, and the base extending through the access opening. The retractor is operated to retract the second ultrasonic transducer so that the two ultrasonic transducers may be moved laterally across the interior surface and the exterior surface, and then released so that the two ultrasonic transducers are in a facing relation to each other with the piece of composite material captured therebetween. Optionally, a coupling medium, such as water, a jell, or oil, may be placed onto the composite material or onto the faces of the transducers, to aid in coupling the ultrasonic signal between the transducer and the composite material. The ultrasonic transducers are operated to send an ultrasonic signal from one of the ultrasonic transducers to the other of the ultrasonic transducers.
The present approach provides a convenient approach to positioning two ultrasonic transducers in precise alignment on the opposite faces of a workpiece which is otherwise difficult to access, with a lightweight, hand-held apparatus. The regions of a composite workpiece around the periphery of an access opening are particularly susceptible to delamination failures between the plies of composite material that are laminated together to form the composite structure, as well as other types of flaws. The apparatus allows the transducers to be quickly and accurately positioned near the access opening, so that ultrasonic measurements may be readily made without any disassembly. This capability not only reduces inspection time and cost, but also increases the frequency at which inspections may be made, an important safety consideration. Inspections conducted over a period of time allow the useful lifetime of the part to be estimated.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.